This invention relates to an attracting nozzle control apparatus for a chip mounting machine and, more particularly, to an improved method of detecting when components are properly picked up by the apparatus.
There are a wide variety of applications wherein components are picked up from a feed section where they are delivered and moved to and placed at an accurate location. A wide variety of devices are employed for actually picking up the components. Frequently such pick-up devices employ vacuum nozzles for picking up the components.
A specific application for this type of apparatus and method is in the making of printed circuit boards. With such printed circuit boards, it is common to employ a device called a "chip mounter" that picks up small components such as integrated circuits, resistors or capacitors at a feed section and places them on a printed circuit board. Vacuum nozzles are frequently employed as the pick-up devices.
The criticality for accurately mounting such components is readily apparent. However, in the process of mounting the nozzle, mistakes may be made even if the apparatus functions automatically and these mistakes can result in inaccurate mounting of the components and other problems.
In addition to the problems of pick-up misorientation, frequently it is possible that the pick-up device will pick up the component not only at an orientation other than desired but the component actually picked up in a manner which is "not normal" (i.e., a manner which will not permit the component to be reoriented into a position which will allow it to be mounted on an accurate location on a substrate). For example, the component normally has a lower surface that is intended to be positioned on the device in which it is to be mounted such as a printed circuit board or the like. However, if the component is picked up off center it may actually rotate from the normal orientation so that the surface that is to be mounted will not be facing downwardly. If an attempt is made to mount the component in this orientation, damage can result. If, however, separate measurements need be taken both to determine the orientation of the article as picked up and also whether the article has been picked up in a normal manner, the speed of the machine can be slowed considerably.
The copending application of the inventor hereof entitled "Method for Mounting Components and Apparatus Therefor," Ser. No. 08/103 358 filed Aug. 9, 1993 and assigned to the Assignee hereof, which is hereby incorporated herein by reference, discloses a method for determining when a pickup which is not normal has occurred without the need for additional measurements being taken.
Specifically, the application discloses a method in which the component is recognized as not having been picked up in a normal manner if the determined minimum length of the component is less than the length of the shorter side of the component times one minus a safety factor, or if the minimum length is greater than the length of the longer side of the component times one plus a safety factor. An additional calculation is likewise disclosed to address situations where the minimum length of the component is not substantially greater than the thickness of the component.
While the foregoing method was a significant advance and is successful in identifying cases where components are not picked up in a normal manner, there are limitations to the accuracy of the foregoing method due to limits in the accuracy of the determination of the minimum length of the component.